Sunday, 17 July 2011

In flux.

I've been a sceptic of the idea that the Arctic will have a virtually sea-ice free minimum this decade, I've said elsewhere that I think it will happen next decade at the earliest. Now I find myself questioning my position.
One of the main arguments on the web is that if one extends the volume trends shown by the PIOMAS they suggest that in summer the volume could reach zero by around 2016, e.g.

If you do the same with the winter trends you get a sea ice free state some time in the 2030s! Yet the sun still sets around September and rises in March, that will still happen in the 2030s, so during that cold winter period the ice will still freeze. Remember that this is a statistical extrapolation, so one can't support it by relying on changes one thinks will happen, e.g. Abbot & Tzipperman 2008. The statistics are based upon what's going in the period of data from which the trends are drawn. So for a start I think that if there's something fishy about what that technique says about winter, why trust it about the summer?

What I think(thought?) will happen is that as the ice thins and there is more open water at the end of the melt season, more heat will be vented to the atmosphere, and thence radiated to space. Furthermore thinner ice allows more conduction of ocean heat to the atmosphere open water at the end of the season means more heat is lost during the freeze to the atmosphere and in the freezing of new ice [EDIT - the perils of posting too late at night]. This is a powerful feedback called sea-ice thickness feedback. This loss of energy should cause:

1) No rapid transition to a seasonally sea-ice free state: Because to a degree the enery lost due to atmosphere/space in winter will partially decouple the energy gains in preceding seasons. So whilst there may be drops ultimately there will be a long tail of lower rate of loss, i.e. gradual loss => rapid loss period => gradual loss. As seen in some climate model simulations e.g. Holland 2006.

2) A reduction of the trend in volume loss as the ice transitions to a mainly FY ice mass. i.e. the sea ice is in transition to a mainly FY sea ice state, this doesn't mean a transition to a sea-ice free state is imminent, even though it may seem so.

However I now see evidence which is causing me to doubt my position and wonder if we are indeed on a fast track to a sea-ice free Arctic sometime this decade.

I hate to rely once again on information from Ron Kwok, but his work of ICESat has been ground breaking and provides crucial information about what's going on in the Arctic. At present it seems to me that Cryosat is overstating sea-ice thickness, so I prefer not to use it.

This page from Kwok provides a neat summary of the key message from Kwok et al 2009 of the 2003. it's as well to click on the graphic to get a larger copy. Kwok et al 2009 "Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008" is referenced in that page, and the publications page is excellent.

Basically what that page from Kwok shows is that the loss of volume has come from the loss of multi-year (MY) sea-ice, not first-year (FY) which has grown to replace the lost MY ice. From my previous post on sea ice thickness this is to be expected in light of the findings of Bitz & Roe: FY ice can grow more quickly than MY, so while MY ice has declined FY sea ice can grow back rapidly in the winter to take it's place. So most of the volume loss as shown by PIOMAS has been from the loss of MY ice volume.

Recently the PIOMAS model volume plot has shown an apparent increase in rate of volume loss.

The most recent information from Kwok about MY sea ice is that the decline has levelled in 2008, 2009 & 2010, PDF. This levelling in the loss of MY sea-ice is what I had been expecting. But not at the same time as volume appears to be assuming a steeper rate of decline!

Then there is this year. I've downloaded all of the false-colour Bremmen AMSRE images for July, the critical month in the season as it sets up the ice pack for the rest of the melt. Running them as a slide show is staggering, even though I've followed previous years. The PIOMAS projection for 2011 uses 7 ensemble members that are hindcast with the weather of the past 7 years, the hindcast period runs up to the end of June, forecast from 1 July 2011. So that projection doesn't take into account the losses of July due to clear skies. Furthermore current forecasts imply that an Arctic Dipole type configuration may be about to replace the zonal high pressure, if so this will draw in warmer air from lower lattitudes into the Arctic Basin. A high rate of loss is to be expected now, and the rate will decline shortly: But the area rate will be acting upon a 'circle' of smaller and smaller radius. In terms of previous years we are currently closest to 2007.

Even allowing for the possibly imminent cloudier conditions, I now suspect that years of volume loss combined with the preconditioning of the first 2 weeks of July mean that the Arctic is now set up to meet or exceed the crash of 2007.

10 comments:

I'm trying to understand how we get from A to B. In this case A is the present state of Arctic sea ice and B is the future state that is at least seasonally ice free.

I can think of several possibilities. Of course it all boils (sic) down to losing more ice each year than is created. The details of the most likely scenario are what escape me.

Simply warm it up? Increasing temperatures will increase loss and inhibit formation. Sort of a 'slow but steady' approach. This seems in-line with predictions that project a seasonally ice free Arctic circa 2070.

Divide and conquer? The ice pack seems not only thinner, but more fractured. Given equal volume, many smaller pieces should melt more quickly than several large pieces. I don't know if models parameterize this - or if the data even supports my assumption.

The knockout punch? One of those 'once every 500 years' heatwave summers where the perfect storm (sic) coalesces; heat, wind, and wave join forces to simply make it all go away.

My rather uneducated view is that we'll see an extension of the 'melt' season into October as latent heat built up over the summer inhibits new ice formation resulting in a lot of thin FYI. Eventually the initial starting conditions for summer will reach a point where a 'warm' winter is followed by a warm melt season and finishes off the remaining (mostly FY) ice.

The analysis you are making is sound, but I do not believe there is a sufficient data to back up the analysis.

The PIOMAS modeled volume loss is not showing up in a proportionate fashion in the extent or area charts. Without direct measurements showing that it is the thinning of first year ice that is causing the volume decline, I do not think you should assume it is in decline.

It does not take much ice volume to generate a large area/extent of first year ice. I do not have the exact volume figure for 2010, but assuming it was 4,000 km3, that was still sufficient ice to create an extent of 4.60 million km2 (per NSIDC). If all of the ice were the same thickness, it would be .87 meters thick.

The ice volume chart at PIOMAS is in excess of 12,000 km3 at June 30, with extent at June 30 of 9.54 million km2 (per NSIDC). Thus, there is plenty of ice volume to generate ice extent/area numbers.

While the trend in ice volume anomaly graph looks steep, there is no indication that it will continue on this slope. In 2010 there was an equally steep drop that was followed by an equally sharp increase in the anomaly. The volume anomaly graph in 2010 reversed course prior to the September minimum. This appears to be a pattern that has been repeated in other years.

At this point, it is weather that will determine if 2011 is below 2010, not climate.

It's a very interesting and useful model study. Upon re-reading it at lunch I did remember it and for anyone with a position of scepticism about an early transition of the Arctic sea ice it's supportive. The graph in figure 3a is particularly instructive.

Basically I think the last few years (since 2007) have probably provided observational evidence that suggests this paper's key message is correct: That after a severe episode of open ocean in the Arctic the ice is able to bounce back. That suggests that there is no area/extent tipping point. I've read several studies using conceptual models of varying degrees of complexity that do not find evidence of a tipping point, the paper addresses those.

The study removes Arctic sea ice in July, and finds that during the following part of the summer there's a net increase of shortwave at the top of the atmosphere (as 'net' is downwards minus upwards insolation, removing the ice massively reduces reflection, so the net goes up). This net increase of shortwave warms the ocean substantially, but the warming is limited to the upper 50 metres. Then during the freeze season, as the ice forms it emits heat, and heat is emitted from the ocean, this heat is lost due to reduction of transport into the region and emission in space during the winter. Tietsche also finds that in the extreme cases they examine the ice has begun to recover after 2 years.

This is an extreme case, but the general process is familiar. In 2007 the ocean remained open in Beaufort well into October, IIRC the Polar Stern reported storms keeping the sea free of ice in the Beaufort sea. So in 2007 arguably we were seeing an effect similar to that the paper outlines - the loss of accumulated energy into the atmosphere. And in the following years we have not seen the energy gained in 2007 manifest itself. As far as I understand the impacts have been due to the loss of volume, not the 'real' heat gained in 2007, which has long since dissipated.

Where I disagree with Tietsche's results is that I suspect the timescale of decadal ice loss is too long. I expect the first virtually* seasonally sea ice free summer will probably be next decade, not this one (although as I say in the main post - I am 'in flux' on this issue).

As for what we'll see as the Arctic transitions to a seasonally sea ice free state, here's my best guess:1) The first seasonally sea ice free state will be followed by a summer that ends with sea ice.2) There will be more crashes like 2007 before that occurs.3) I expect the overall profile of the ice extent/area to be similar to what's seen in Holland 2006 figure 1 (link to pdf at end of main post). However I think it will be compressed in the time domain such that regular sea ice free state will occur well before 2070 (not sure when - 2030s?). Winters will continue to produce a lot of FY ice, unless some new factor turns out to be correct (e.g. Abbot & Tzipperman - see main post).

Could be worth expanding upon and doing a post...

*By 'virtually sea ice free' I mean less than 1 million km^2 off the coast of the Canadian Arctic Archipelago and Greenland.

Thanks for the comment. It's worth bearing in mind that the massive loss of thickness/volume since the 1970s (see my 2 earlier posts) hasn't shown up in the extent or area. NSIDC state "Average ice extent for June 2011 was 11.01 million square kilometers..." Sea Ice News 6/7/11. PIOMAS volume for June is about 15,000 km ^ 3. So 15x10^3/11x10^6 = 1.36x10^-3 or ~1.4metres thick. There are differences in area covered between PIOMAS and NSIDC but by June these should mostly be outside the sea-ice so can be neglected(?). That's in June before the melt of early July set in, and the PIOMAS projection for this year (see main post) also doesn't take into account this month. Maslowski states that for 2003 to 2006 first year ice was typically 1.5m thick.

Leaving aside my problem with the cessation of loss of MY ice while volume appears to be declining, on balance my reasoned postion still is that volume loss will level, as will loss of MY ice. I expect this because the winter is still cold enough to fill the basin with FY ice which grows fast, that's why I raised the Bitz paper in "The loss of multi-year sea ice Part 2." I see the rapid volume loss in the last decade as being part of a process of final transition to a mainly FY ice pack, not as the herald of the total demise of the sea-ice.

I agree that normally we'd expect weather to be the dominant factor, and accept that this may be the case this year. It's quite possible that weather could slow the rate of loss and give us a mundane extent in September, mundane in the post 2007 regime. Indeed back in June I voted over at Neven's for between 4.5 and 5 million. However given the apparent thinness of the pack, and given the clear skies and rapid recession in July, I now think that on balance the ice has been pre-conditioned and that this summer we stand the best chance since 2007 of seeing that year beaten.

I agree there is a problem with the cessation of loss of MY ice (or possibly an increase in MY ice) while the PIOMAS volume appears to be declining, which would mean that it is first year ice that is suffering volume/thickness decline, but the problem may be with the PIOMAS model and not first year ice.

I would prefer to see examples of direct measurement showing thinning of first year ice before joining the chicken little band wagon proclaiming an imminent ice free Arctic at the minimum (or an Arctic below 500,000 km2 in the next three years) or endorsing those who predict a sudden and complete collapse of Arctic sea ice.

Keep up the good work of bringing information and studies about the state of Arctic ice to your blog.

It may be counter-intuitive, but decreasing volume and steady or increasing extent/area/MYI are not contradictory.

I've been interested in watching the 30-day gifs from the new PIPS/CICE site. In particular the Ice Thickness animation.

After watching the Ice Thickness map look at the CT Sea Ice Concentration map. It's quickly apparent that very little of the thickest ice is in high concentration areas.

It should also be remembered that if only 15% of a pixel/grid is MYI it gets coded MYI for the entire pixel/grid - similar to sea ice extent. So, a large area may be considered MYI, but of lesser 'quality' if we consider a full range of quantitative and qualitative factors.

Considering the hundreds of gigatons that are melting off the Greenland icesheet and the Canadian Archipelago each year, it would seem only logical that Arctic sea ice would be losing comparable volumes - if not more.

Check out the thickness on PIPS (here), especially in the Beuafort sea. It looks very thick given the state of the ice-edge in Beaufort. Furthermore most of the FY sea-ice is shown to be between 2 and 2.5 metres.

In light of the evidence I present in my 2 earlier posts on MY sea ice thickness. Personally I suspect PIPS is giving an overestimate of thickness. PIOMAS seems more reasonable to me.

However I don't throw the baby out with the bathwater. PIPS is showing what is to be expected in terms of thickness change patterns.

Hi Chris, good to see a very informed blog that I will definitely follow.

Most of the research I have seen predicts ice free summers between 2030 and 2050. Though 2050 seems very optimistic given recent melting.

The WTFUWT blog is sort of running a book on predictions which will no doubt be used in a future post to poo poo the science;http://wattsupwiththat.com/2011/07/16/i-need-your-help-for-a-short-research-project/#more-43544

If I was to give an uneducated guess, given that this year could be a new record low and the last one was only four years ago, and both passages being navigable for several years in a row, I'd say that the Arctic could very well be virtually ice free by the end of this decade.

I'm just finishing off a post about why, despite the doubt I express in the main post here, basically I'm still very sceptical of seeing a sea-ice free state this decade. I should be posting later today.